Systematic variations in critical dimension feature size of lithographically defined images may sometimes be required to compensate for process variability in the semiconductor industry. Currently, the prior art addresses only the elimination of systematic variation such as U.S. Pat. No. 6,331,711. Such techniques, however, are subject to the limitation of the mask writing tool address grid (spot size) when determining the minimum possible critical dimension difference within a pattern.
Consequently, a need exists for a method which permits a virtually continuous variation of feature size by superimposing two exposures that are identical except for their distortion terms; that is to say magnification, rotation, translation and the like.